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time precession Two-site conformational exchange In the absence of exchange, magnetization remains in phase

6
Conformational exchange on the millisecond timescale leads to dephasing of the signal. Peaks become broad or even disappear. The signal decays (relaxes) more rapidly. time precession Two-site conformational exchange

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Two state fitting: T4 lysozyme L99A We could just average p B values over all residues, but there are several drawbacks: –The average value of p B will not in general correspond to a best fit to experimental data. –It is difficult to identify residues that do not participate in the global process. –Residues in fast exchange do not provide p B, however k ex is global, refines the fit. p A p B (Δω) 2 k ex p B Δωk ex fast exchangeintermediate exchange

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Structures of invisible states Match reconstructed spectrum to reference state with known spectrum: –unfolded state –ligand-bound state –phosphorylated form –etc. state C is the unfolded state Δω A-random coil Δω AC 1H1H 15 N Mittermaier, Korzhnev & Kay Biochemistry